I don't know of any hops that are not bitter, though you can see there relative bitterness by looking at their %aa (% alpha acid). The lower the %aa, the less bitter, so hops at 12%aa will be very bitter and at 3%, less so. One thing you may be able to find are aged hops, that have lost much of their bitterness with time. Or, you could try buying hops and aging them, but be aware that hop flavor changes with age, too.